Historically, synthetic fibers for use in apparel, including polyester fibers, have generally been supplied to the textile industry for use in fabrics and garments with the object of more or less duplicating and/or improving on natural fibers. For many years, commercial synthetic textile filaments, such as were made and used for apparel, were mostly of deniers per filament (dpf) in a similar range to those of the commoner natural fibers; i.e., cotton and wool. More recently, however, polyester filaments have been available commercially in a range of dpf similar to that of natural silk, i.e. of the order of 1 dpf, and even in sub deniers, i.e., less than about 1 dpf, despite the increased cost. Various reasons have been given for the recent commercial interest in such lower dpfs, such as about 1 dpf, or even sub deniers.
Our so-called "parent application"(No. 07/647,371 now abandoned), and U.S. Pat. No. 5,250,245 the disclosure of which is hereby incorporated herein by reference, was concerned with the preparation of fine filaments by a novel direct melt spinning/winding process, in contrast with prior processes of first spinning larger filaments which then needed to be further processed, in a coupled or a separate (split) process involving drawing, to obtain the desired filaments of reduced denier with properties suitable for use in textiles. The filaments of the "parent application" are "spin-oriented"; that is, produced as "undrawn" filaments. The significance of this is discussed in the art and hereinafter.
We have found that consumer reaction to fine filament textile (flat or textured) yarns (all filaments being of the same cross-section and of the same denier, and especially wherein the filaments are of denier less than about 1), has tended to limit their use to selected textile fabrics where fabric "body" and "drape" has not been important or where providing such fabric "body" and "drape" through twisting of the multi-filament yarns and/or change in fabric construction is too expensive for the particular end-use and/or where such changes adversely affect other properties (such as visual and tactile aesthetics) that make such fabrics undesirable. It would be desirable to make fine textile fabrics with desired "body" and "drape" from fine filament yarns without twisting of the fine filament yarns and/or change in fabric construction. It would also be desirable to provide spin-oriented undrawn fine filament yarns that, depending on their combination of properties, can be used as direct-use yarns or as draw feed yarns (e.g., to provide drawn flat yarns or textured "bulky" yarns) that can provide fabric "body" and "drape" without having to incur costly yarn twisting, for example, and without having to change fabric construction and compromise visual and tactile fabric aesthetics.
It is important to maintain uniformity, both along-end and between the various spin-oriented filaments and drawn filaments therefrom. Lack of uniformity often shows up in the eventual dyed fabrics as dyeing defects, so is undesirable.
For textile purposes, a "textile yarn" must have certain properties, such as sufficiently high modulus and yield point, and sufficiently low shrinkage, which have distinguished conventional textile yarns from conventional "feed yarns" that have required further processing to provide the minimum properties required for making textiles and subsequent use. Generally, herein, we refer to untextured filament yarns as "flat yarns" and to undrawn flat filament yarns by terms such as "feed" or "draw-feed" yarns. Filament yarns which can be used as a textile yarn without need for further drawing and/or heat treatment are referred herein as "direct-use yarns".
It is important to recognize that what is important for any particular end-use is the combination of all the properties of the specific yarn (or filament), sometimes in the yarn itself during processing, but also in the eventual fabric or garment of which it is a component. It is easy, for instance, to reduce shrinkage by a processing treatment, but this modification is generally accompanied by other changes, so it is the combination or balance of properties of any filament (or staple fiber) that is important. It is also understood that the filaments may be supplied and/or processed according to the invention in the form of a yarn or as a bundle of filaments that does not necessarily have the coherency of a true "yarn", but for convenience herein a plurality of filaments may often be referred to as a "yarn" or "bundle", without intending specific limitation by such term. It will be recognized that, where appropriate, the technology may apply also to polyester filaments in other forms, such as tows, which may then be converted into staple fiber, and used as such in accordance with the balance of properties that is desirable and may be achieved as taught hereinafter.